This is an old DIY, but it's so Halloween-y that I thought I'd share it anyway. These are actually prototypes for two bigger ones that I made for a friend's birthday present. It's just two ceramic pots I got at a flea market covered in modelling clay. I tried the plastic kind, but it was really hard to use, so I just used the normal stuff and let these air dry. Then I painted them with a rock texture paint from the local craft store. The paint had little grains in it, which makes the surface even feel rock-like. The details I did with a toothpick while the clay was still soft. The paint is water based, so you can't wash these, but wiping with a wet cloth is okay.
This is a super easy project, maybe a few hours in total, not counting the time it takes for the clay and paint to dry. Plenty of time to finish before Halloween, if inspiration strikes you.